The invention relates generally to adhesion promoters, electroactive devices comprising the same, and methods. In one embodiment the invention relates particularly to adhesion promoters between layers in a multilayered electroactive device comprising at least one electroactive organic layer.
Many electroactive devices including opto-electronic devices, organic light emitting devices, electroluminescent devices, photovoltaics, and organic thin film transistors have two or more layers of organic or inorganic materials, or a combination of such layers. Desirably the performance of these devices can be enhanced by improving the mechanical stability of these layers. Improved adhesion between layers may help improve the mechanical stability while reducing the interfacial electrical resistance. A particularly difficult problem is the adhesion between inorganic and organic layers in such devices. For example, adhesion of a titanium dioxide layer to a plastic layer or of a light emitting polymer layer to a cathode metal layer often presents problems.
Most of the state-of-the-art organic light emitting devices (OLED) are composed of multilayers. An illustrative multilayer OLED may be represented as: ITO//HTL//LEP//Cathode where ITO is an anode comprising indium tin oxide, HTL is a hole-transporting layer, LEP is a light emitting polymer and the cathode may be one of a low work function metal such as, but not limited to, Al or Ca. Layers can be deposited via vapor methods or from solution by spin coating, dip coating, and like methods. An illustrative photovoltaic device (PV) employs a dye-coated metal oxide like titanium dioxide to absorb light and separate charges from the dye excited state. For example, TiO2 may be deposited on a conducting metal oxide like ITO. Device performance for these and other electroactive devices depends on formation of intimate contacts between the layers and the capability of maintaining the intimate contacts, which is particularly critical for flexible substrates and devices. It would therefore be desirable to find methods and device structures that have, among other properties, improved adhesion between layers in a multilayered device. It would also be desirable to identify efficient adhesion promoters to provide said adhesion.